Fluoroelastomers with low glass transition temperatures are typically utilized as sealing material for low temperature applications. Most of the commercially available low temperature elastomers are copolymers or terpolymers based on VDF and/or TFE and perfluoromethyl vinylether (PMVE). PMVE is often selected as a comonomer due to its favorable copolymerization properties. Some conventional elastomers have glass transition temperatures (Tg's) of around −30° C., but the solvent resistance (e.g. MeOH swell) is often sacrificed in order to obtain desirably low Tg's.
To improve the solvent resistance, it is generally recognized within the art that a proportion of tetrafluoroethylene or perfluoro(alkyl vinyl ether) to be copolymerized should be increased. Further perfluoro(alkyl vinyl ethers) itself are expensive monomers and a cost increase of the fluoropolymer and fluoroelastomer products is inevitable by use of an increased amount of perfluoro(alkyl vinyl ethers).
Various approaches have been made to lower the Tg of the fluoropolymers and fluoroelastomers while maintaining or improving other properties. Many of these approaches end up in unacceptable comonomer incorporation, extremely long polymerization run times (e.g. up to 17 hours), undesirable solvent resistance, and high comonomer costs.
U.S. Pat. No. 6,380,337 describes co- and quad-polymers comprising: 65 to 85 mol % VDF, 0.5 to 30 mol % perfluoromethoxypropyl vinyl ether (MV31), and optionally 0 to 10 mol % TFE and 0 to 25 mol % of a perfluorovinylether (preferably PMVE). The patent describes resulting elastomers with Tg's of about −42° C. However, the resulting elastomers do not possess a desirably low solvent resistance over extended testing durations.
The present invention is directed to fluoropolymers and fluoroelastomers with a desirable balance between Tg, sufficient solvent swell (<60%) and an economical polymerization process.